1. Field of the Invention
The present invention relates to an image processing apparatus.
2. Description of the Related Art
Recently, to increase the speed of image formation in an electrophotographic method color image processing apparatus (hereinafter, an “MFP” (multifunction peripheral)) and to improve image quality, in an MFP system, it has become necessary to transfer data that exceeds several hundred Mbytes (megabytes), to a memory such as a dynamic random access memory (DRAM).
The amount of data that a memory such as a DRAM can transfer in a fixed period is limited. Trying to transfer a large amount of data may exceed the DRAM's data transfer capability, so that the performance which the MFP requires cannot be satisfied.
Conventionally, to ensure that the DRAM data transfer capability is not exceeded, the amount of data to be transferred to the DRAM is reduced by coding a raster image of about 600 dpi obtained after rasterizing scanner data or page description language (PDL) data. However, to reduce the amount of data by image coding, coding methods such as lossy compression, represented by Joint Photographic Experts Group (JPEG) compression, in which the image is not completely returned to its original state, were mainstream.
Subsequently, a method was proposed that combined a lossless compression method, represented by JPEG-LS, and a lossy compression image coding method. Thus, Japanese Patent Application Laid-Open No. 2003-69835 realizes a high printing performance by reducing the amount of data in the system by combining the characteristics of a lossy compression method (JPEG) and a lossless compression method (JPEG-LS). When lossless and lossy compression methods are combined, the target image is simultaneously subjected to two coding methods, and the data from the method that has the smaller coded data amount is selected. At this point, the coded data that was not selected is automatically discarded.
Lossless compression methods have continued to evolve, and have now reached the stage where, as discussed in Japanese Patent Application Laid-Open No. 2006-229688, for example, image coding can be performed after determining in advance whether a lossless compression method or a lossy compression method should be used to generate intermediate compression data. Further, by employing the method discussed in Japanese Patent Application Laid-Open No. 2008-42681, two coding circuits can operate individually, thereby obviating the need to discard unused coded data.
In Japanese Patent Application Laid-Open No. 2006-229688, several pixels are grouped into a block in advance, and that block is used as a coded data region by collecting the original image data of the coded data region. A determination is then made regarding whether the pixel information for the coded data region is a picture image represented by a natural image, or a graphic image represented by a computer graphic. Based on the determined result, image coding is performed by an image coding circuit like that discussed in Japanese Patent Application Laid-Open No. 2006-229688.
Thus, the technique used in Japanese Patent Application Laid-Open No. 2006-229688 requires two types of circuit, a lossless compression circuit and a lossy compression circuit. Coding can be performed by determining in advance whether lossless compression or lossy compression is more appropriate, and operating one of the two kinds of compression circuit.
However, in Japanese Patent Application Laid-Open No. 2006-229688, if there is a succession of coded data groups for which lossless compression is appropriate, one of the two coding circuit types comes to a complete standstill. Accordingly, an improvement in performance may not be obtained even if the two types of coding circuit are configured in parallel. Consequently, even if the image coding method is determined in advance, an increase in system speed may not be obtained.